Canister, sealing method and composition for sealing a borehole

ABSTRACT

Method and composition for sealing a borehole. A chemically bonded phosphate ceramic sealant for sealing, stabilizing, or plugging boreholes is prepared by combining an oxide or hydroxide and a phosphate with water to form slurry. The slurry is introduced into the borehole where the seal, stabilization or plug is desired, and then allowed to set up to form the high strength, minimally porous sealant, which binds strongly to itself and to underground formations, steel and ceramics.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/510,663 filed on Feb. 22, 2000 and claims thebenefit of U.S. Provisional Application No. 60/131,752 filed on Apr. 30,1999, both of which are hereby incorporated by reference.

STATEMENT REGARDING FEDERAL RIGHTS

[0002] This invention was made with government support under ContractNos. W-7405-ENG-36 and W-31-109-ENG-38 awarded by the U.S. Department ofEnergy. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0003] This invention relates to methods of sealing or stabilizingboreholes and compositions for sealing or stabilizing boreholes.

BACKGROUND OF THE INVENTION

[0004] When holes are being drilled for exploration, rock and soilsampling, water, oil, gas, or geothermal developments, there is often aneed to seal or stabilize the walls of the borehole, cement in casingpipes, or seal portions of the well at some depths while other portionsat other depths are treated or produced. Drilling programs formultilateral, horizontal or deviated wells often require that portionsof a wellbore be sealed or plugged. Also, after casing, the elbow areaswhere lateral wellbores depart from the vertical hole are often thesites of loss of fluids into the surrounding formation. This fluid lossis often caused by high pressures encountered in the deviated productionpath, and exacerbated by mechanical failures of bonding materials at thelateral junction.

[0005] Drilling-related problems such as lost circulation, watershutoff, and swelling, sloughing or caving of the borehole walls havebeen dealt with by introducing various materials into the borehole toseal or stabilize the borehole, or to clog pores or fractures in thesurrounding rock formation or to fill and stabilize cavities orwashouts. These materials include various fibrous materials added to thedrilling fluid or cement compounded with various additives.

[0006] Generally, cement-based materials do not bond well to the earthmaterials penetrated by the borehole and often do not stay in place. Inaddition, there are often problems getting these materials applied atprecisely the desired depths and adapted to the particular downholeconditions in the trouble zone, particularly in severe lost circulationsituations where cement materials tend to be overdisplaced away from thenear-wellbore region. Further, with cement-type materials there can bedifficulty judging appropriate pumping times and setting times at theelevated temperatures that are encountered in geothermal or very-deeppetroleum drilling situations.

[0007] Furthermore, if the formation or fracture zone is severelyunderpressured or the formation contains large open porosity (e.g.,interconnected large solution cavities in limestone formations), sealingthe trouble zone by injecting cement from the surface is oftenunsuccessful. It is often unsuccessful no matter how many times thesealing operation is repeated because the hydrostatic head of the cementslurry causes the cement to be overdisplaced (i.e., carried away) fromthe near-wellbore region where the sealing is desired.

[0008] Another common approach used when there is a need to seal theborehole at certain depths while drilling is to circulate drilling fluid(mud) containing lost-circulation material to affect atemporary-to-permanent seal of the borehole wall as the drilling fluidpermeates the formation or fracture zone. However, fibrouslost-circulation materials being carried in the drilling fluid may notadequately bridge-off the fractures or fill the open porosity because ofthe large outward pressure gradient from the overpressured borehole intothe severely underpressured formation. This condition is referred to assevere lost circulation.

[0009] When there is a need to stabilize poorly consolidated or looseand friable formations at certain depths, where caving or sloughingproduces cavities (“wash-outs”) and attendant borehole stabilityproblems, this again has traditionally been done by pumping portlandcement from the surface to fill and stabilize the borehole.Subsequently, the borehole is redrilled through the soft cement plug anddrilling then continued. However, since portland cement does not adherewell to most geologic materials, the typical result is to “wash” thecement out of the borehole and cavity while redrilling. With the cementwashed out of the borehole, the cavity is reopened and additional cavingor sloughing occurs. Then, the cementing operation is repeated overagain until either a good plug is finally established, or the operatorfinally resorts to running and cementing a string of steel casing pipethrough the trouble zone. Running casing reduces the size of the holethat can be drilled below the cased-off interval.

[0010] When there is a need to stabilize and support the wellbore atcertain depths where squeezing (i.e., plastic deformation and flowing offormations such as serpentines or plastic clays) is encountered, theonly engineering solution has been to finish the drilling (often withmultiple redrilling or reaming operations) as fast as possible, then runand cement a string of casing across the trouble zone. This remedialsolution relies on the collapse strength of the casing to hold back thesqueezing formation and reduces the size of the hole that can be drilledbelow the cased-off interval.

[0011] Similarly, when swelling clay (hydrating) formations areencountered in drilling, the standard remedial approach is to preventwater-based fluids from penetrating or reacting with the clays andcausing swelling by: (a) forming an impervious “wall cake” on the wallof the borehole; or (b) adding potassium chloride to the drilling fluidto make it less reactive with the clays; or (c) switching to ahydrocarbon-based drilling fluid, which is, however, generallyundesirable because of increased costs, difficulties of cleanup andenvironmental hazards. Again, casing off the trouble zone is a typicalsolution.

[0012] Thus there is still a need for effective ways of sealing,stabilizing or plugging boreholes under severe conditions. There is alsoa need for sealing, stabilizing and plugging materials with a capabilityfor bonding tightly to earth materials, steel casing and to the sealing,stabilizing and plugging materials themselves. There is a further needfor materials that can be tailored for the downhole conditionsassociated with the problem to be remedied and that can be applied toprecisely the selected depths.

[0013] Therefore, it is an object of this invention to provide acomposition and method for sealing, stabilizing or plugging boreholes atselected depths.

[0014] It is another object of this invention to provide a compositionfor sealing, stabilizing or plugging boreholes that can be tailored tothe viscosities and setting temperatures mandated by downhole conditionswithout compromising the properties of the cured material.

[0015] It is a further object of this invention to provide a compositionfor sealing, stabilizing or plugging boreholes that binds strongly tothe composition itself and to underground formations, steel andceramics.

[0016] It is yet a further object of this invention to provide acomposition and method of making the composition for sealing,stabilizing, supporting and plugging lateral junctions in multilateralboreholes.

[0017] It is also an object of this invention to provide a compositionand method of making compositions for sealing, stabilizing or pluggingapplications in offshore drilling operations.

[0018] It is yet another object of this invention to provide a method ofapplying the invention compositions for sealing, stabilizing or pluggingboreholes downhole.

[0019] Additional objects, advantages and novel features of theinvention will be set forth in part in the description that follows, andin part will become apparent to those skilled in the art uponexamination of the following or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

SUMMARY OF THE INVENTION

[0020] To achieve the foregoing and other objects, and in accordancewith the purposes of the present invention as embodied and broadlydescribed herein, the invention includes a method of sealing,stabilizing or plugging boreholes by extruding or otherwise applying anslurry of oxide or hydroxide, phosphate, and water into the place wherea plug, seal or borehole stabilization is desired, then allowing it tocure to form a high strength, minimally porous, chemically bondedphosphate ceramic material that binds strongly to itself, undergroundformations, steel and other ceramics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and form apart of the specification, illustrate embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention.

[0022] In the Figures:

[0023]FIG. 1 is a schematic of an example of how the borehole sealantcan be applied downhole using a canister lowered on a wire line;

[0024]FIG. 2 is a schematic of use of a canister on coiled tubing toapply the invention sealant in an underreamed section of a wellbore in azone of swelling or squeezing clays or plastically deforming materials;

[0025]FIG. 3 is a schematic showing a canister run on coiled tubing toapply the invention sealant in a wellbore with caverns or washouts;

[0026]FIG. 4 is a schematic representation of the invention repairing azone of a loose formation in which a cavern or wash-out has occurred;

[0027]FIG. 5 is a graph of compression strength of invention slurry as afunction of time;

[0028]FIGS. 6a and 6 b are schematics of diversion in a cased andperforated vertical well using the invention sealant and method ofapplication;

[0029]FIG. 7 is a schematic of a multilateral borehole showing thelocation where invention sealant is applied;

[0030]FIG. 8 is a schematic of use of the invention sealant and methodin a well with a slotted liner horizontal completion;

[0031]FIG. 9 is a graph of the setting time of an invention sealant as afunction of temperature; and

[0032]FIG. 10 is a photograph of a sandstone surface sealed with aninvention sealant.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The invention includes a chemically bonded phosphate ceramicmaterial that can be used for sealing, stabilizing or pluggingboreholes. In the present invention, oxides or hydroxides of variouselements are combined with phosphoric acid or water-soluble phosphatesto form slurry. The slurry is applied to a target area where it sets upto form a sealant that is an effective nonporous seal, formation binderor borehole plug.

[0034] The formulations of the invention can be varied to obtain a broadrange of selected slurry viscosities, setting times, and sealantproperties.

[0035] By varying the cation in the chemical mixture of the invention orby adjusting the phosphoric acid content, a wide range of setting timesat different temperatures can be achieved and controlled. The inventionslurries will set up or cure even in water, drilling fluids, salt wateror seawater.

[0036] The borehole sealants of this invention adhere tightly to mosttypes of rocks, including sands, shales, clays and limestone, and otherearth materials typically encountered while drilling, even when therocks are water-saturated and are at typical subsurface temperatures.The sealants will also adhere to steel wellbore casing materials and toother ceramics or the sealants themselves if placed sequentially instages.

[0037] Oxides or hydroxides that are useful in the practice of theinvention are those that are sparsely soluble and that do not reactuncontrollably. These oxides and hydroxides include, but are not limitedto, MgO, MnO, Al(OH)₃, Al₂O₃, FeO, Fe₂O₃, Fe₃O₄, ZnO, Zr(OH)₄, ZrO₂,Y₂O₃, La₂O₃, VO₃, CrO, CoO, PbO, Nd₂O₃, TiO₂, CaSiO₃. CaO can also beused if it is used in combination with phosphates such as Ca(H₂PO₄).Preferred oxides include magnesium oxide and zinc oxide.

[0038] Oxides or hydroxides in powder form with particle sizes in therange between about 2 microns and about 100 microns are preferredbecause reaction rates of smaller particles are difficult to control andcoarser particles result in slurries that are too viscous.

[0039] A stoichiometric amount of oxide or hydroxide relative to theamount of phosphate is preferable for efficient reactions. An amount inthe range from about 18 to about 60 weight percent, based upon totalweight of oxide or hydroxide and phosphate, is generally useful in theinvention. More preferable is an amount of oxide or hydroxide in therange from about 20 to about 50 weight percent. Generally presentlypreferred is an amount of oxide or hydroxide in the range from about 22weight percent to about 34 weight percent. Use of too little oxide orhydroxide will result in slurries that are too acidic and corrosive tohandle without damaging pumping and other equipment. Use of too muchoxide or hydroxide will cause poor consolidation of the sealant.

[0040] It is believed that incorporation of the phosphates improves thebonding between the sealant and metal, previously applied sealant,sandstone or other oil-saturated earth materials because phosphatesolutions act as detergents on oily surfaces and clean the surfaces oncontact.

[0041] Phosphates that are useful in the practice of the invention arethose that are soluble in water and that will result in the desired pHwhen the slurry is formed.

[0042] Generally, for most applications, a pH in the range from about 3to about 9 is useful. Presently preferred is a pH in the range fromabout 4 to about 8.

[0043] Phosphates that are useful in the invention include those withthe formula

A(H₂PO₄)_(n)

[0044] wherein A=hydrogen, alkali metal, aluminum, calcium or ammoniumion. Presently preferred phosphates include, but are not limited to,phosphoric acid, NaH₂PO₄, KH₂PO₄, (NH₄)H₂PO₄, AlH₃(PO₄)₂, Ca(H₂PO₄)₂,and mixtures thereof. Presently preferred are NaH₂PO₄ and KH₂PO₄ becausethey react well with alkaline oxides, react slowly enough to avoidoverheating, but do not react too fast in setting up of the slurry.

[0045] An amount of phosphate sufficient to react stoichiometricallywith the oxide or hydroxide is needed. An amount in the range from about40 to about 82 weight percent, based upon total weight of oxide orhydroxide and phosphate, is generally useful in the invention. Morepreferable is an amount of phosphate in the range from about 50 to about80 weight percent. Generally presently preferred is an amount ofphosphate in the range from about 66 to about 78 weight percent. Use oftoo little phosphate will result in poor bonding properties of thesealant. Use of too much phosphate will result in slurries that are tooacidic and that do not as readily cure.

[0046] Phosphates in powder form with particle sizes of less than 100micrometers are preferred because they dissolve in water easily andhence are more readily mixed. Coarser crystalline powders can also beused.

[0047] Water is used in the invention mixture, first as a means to formslurry of the oxide or hydroxide powder and phosphate, then as achemical component of the final sealant product that is a hydratedcompound.

[0048] An amount of water sufficient to enable the reaction between theoxide or hydroxide and the phosphate and sufficient to achieve thedesired slurry viscosity is needed. An amount in the range from about 25to about 60 weight percent, based upon total weight of the slurry, isgenerally useful in the invention. More preferable is an amount of waterin the range from about 30 to about 50 weight percent. Generallypresently preferred is an amount of water in the range from about 30 toabout 35 weight percent. Use of too little water may result inoverheating of the slurry, overly rapid curing and poor bonding of thefinal product. Use of too much water will cause the slurry to not set orset very slowly.

[0049] The chemically bonded phosphate ceramic sealants of thisinvention can be used in virtually any chemical and thermal environmentby adjusting the amounts of oxide or hydroxide and phosphates, balancingthe pH and manipulating the setting rate, depending upon the proportionof hydrocarbons; amount of water and its chemistry and pH; and theformation or fluid temperature in the borehole to be sealed.

[0050] The oxide or hydroxide and phosphate components of the inventionslurry can be combined by using any suitable method such as high-shearmixing, or ball milling of the powder components and mixing with thewater.

[0051] The oxide or hydroxide and the phosphate can be combined first,then combined with the water, that can then be added in increments toachieve the desired viscosity and setting rate. Alternatively, eitherthe phosphate or the oxide or hydroxide can be combined with the waterfirst to form slurry that is combined with the remaining majorcomponent.

[0052] It is generally desirable to produce a slurry that is thin enoughto be easily pourable or pumpable for transfer into and thensubsequently out of canisters to be deployed downhole; or pumpablethrough coiled tubing for extruding onto the borehole surfaces to besealed or stabilized or into the borehole interval to be filled orplugged; or through drill pipe and into the borehole interval to besealed, stabilized or plugged.

[0053] The slurry has a viscosity that will enable the slurry todisplace, both outwardly and upwardly, the water-based fluids in thewellbore with minimal intermixing of the two fluids.

[0054] Depending upon the efficiency of the mixing equipment, particlesize, amount of water used, viscosity and temperature, mixing time canrange from a matter of seconds to many hours. A mixing time sufficientto afford adequate contact of the components is required. Generallypreferred are shorter mixing times in the range from about 5 minutes toabout a half hour.

[0055] When it is desired to use additives, then the additives can becombined with either the phosphate or the oxide or hydroxide prior toforming of the slurry, combined with a mixture of the major componentsprior to forming of the slurry, or combined with slurry of one or moreof the major components.

[0056] Additives can be used as needed for facilitating the flow of theinvention slurry, increasing the density of the final product, slowingdown the curing time, enhancing the strength of the final product, orvarying other properties such as porosity or permeability of the finalproduct to tailor it to the specific environment in which it will beused.

[0057] Retardants that prevent the sealant from setting up too quicklycan be incorporated into the invention mixture. Suitable retardantsinclude acids such as boric acid, citric acid, oleic acid andcommercially available organic retardants that contain some inorganiccomponents, such as lignosulfonate.

[0058] Depending upon the retardant chosen, the temperature of the siteto be sealed, and the desired setting time, an amount of retardant inthe range from greater than 0 to about 10 weight percent based on totalweight of the slurry is generally useful in the invention. For example,in a slurry of 100 weight percent, 32 weight percent oxide, 51 weightpercent phosphate and 16 weight percent water, 1 weight percent boricacid slows the setting rate at 90° C. to 20 to 30 minutes.

[0059] Compressive or flexural strength of the chemically bondedphosphate ceramic sealant of this invention can be enhanced by additionof reinforcing materials such as glass fibers; chopped glass strands;mica; silica; aramids; carbon fibers; alumina; hollow glass or silicaspheres; perlite; vermiculite; metal fibers such as aluminum, bronze,zinc, nickel and stainless steel; synthetic organics such as polymerfibers and copolymers; silicate-containing materials such as fly ash;volcanic ash; sand; gravel; other aggregates; and mixtures thereof.

[0060] An amount of reinforcing material sufficient to achieve thedesired improvement in flexural strength or compressive strength isneeded. An amount in the range from greater than 0 to about 15 weightpercent based on total weight of the slurry is generally useful in theinvention. More preferable is an amount of reinforcing material in therange from about 0.5 to about 10 weight percent. Generally presentlypreferred is an amount of reinforcing material in the range from about 1to about 5 weight percent. Use of too little reinforcing material willresult in failure to achieve the desired flexural strength. Use of toomuch reinforcing material may cause undesirably high porosity.

[0061] Additives to decrease porosity and permeability can be used.Glass-forming silicates such as calcium silicate, sodium compounds, flyash, acrylics and other polymer additives are useful, depending uponavailability, particle size and desired porosity or impermeability.Presently preferred for decreasing porosity in the invention sealants iscalcium silicate or class F or C fly ash because of their particulareffectiveness in filling pores in the sealants.

[0062] An amount of permeability-decreasing material sufficient to fillenough open pores to achieve the desired low level of porosity isneeded. An amount in the range from greater than 0 to as much as about80 weight percent is generally useful in the invention for reducingporosity and filling the pores of the invention sealant, depending uponmaterial selected, porosity of the sealant, and desired degree ofimpermeability. For example, when pure materials such as calciumsilicate are used to decrease the sealant permeability, generallypreferable is an amount in the range from about 2 to about 20 weightpercent. When ashes are used, generally preferred is an amount ofpermeability-decreasing material in the range from about 10 to about 70weight percent, based upon total weight of the non-aqueous components.Use of too little permeability-decreasing material will result in moreporosity than desired. Use of too much permeability-decreasing materialcan result in sealants with less strength than desired.

[0063] Surfactants such as gas generating agents, metal oxide expandingagents, or calcium sulfate hemihydrates or mixtures thereof can be addedto form a second phase in the invention slurries to increase theexpansion of the slurries as they set or cure. Any of these surfactantsare considered to be generally effective.

[0064] An amount of surfactant sufficient to give the desired amount ofexpansion of the slurry as it sets is needed. An amount in the rangefrom greater than 0 to about 10 weight percent based upon total weightof the slurry is generally useful in the invention. More preferable isan amount of surfactant in the range from about 0.5 to about 5 weightpercent. Generally presently preferred is an amount of surfactant in therange from about 1 to about 3 weight percent. Use of too littlesurfactant will result in lack of the desired amount of expansion. Useof too much surfactant may cause loss of strength in the cured sealant.

[0065] If desired for economic reasons or to thicken the slurries, anysuitable filler material can be added to the slurry. Cuttings from theborehole, sand, soil, clay or mixtures thereof are presently preferredbecause of ready availability at most drilling sites and economy.

[0066] Typically the powdered components and any additives are premixed,bagged, transported to a drilling site, and then combined with water toform the slurry. Alternatively, the components are transported to adrilling site where the slurries are mixed. Any of the additives can beadded during mixing of the components, either by premixing with one orboth of the powders or by mixing into the slurry.

[0067] The slurries of this invention are flowable, slightly expandable,and rapidly set up into ceramic materials.

[0068] The ceramic downhole slurries of this invention have sufficientlyhigh shear strength to withstand intact the rigors of being pumped andextruded. However, if desired, silicates or other additives can beincorporated into the slurry to alter the flow properties, facilitatingflow of the slurry during pumping and extrusion.

[0069] The invention slurries are unaffected by the presence of salts,salt water, seawater or brine. Therefore, the invention slurries can bemixed on offshore drilling platforms using available seawater.

[0070] The slurries of the invention will become more viscous whensubjected to increased temperatures. Higher viscosity slurries aregenerally more useful so that the slurry will displace, rather than mix,with water or aqueous-based drilling fluid in the downhole environment.

[0071] Slurry for the sealant of this invention can be poured or pumpedinto canisters to be lowered down the borehole or drill pipe on awireline or coiled tubing, or pumped through coiled tubing to theselected location, or pumped directly down through the drill pipe orborehole.

[0072] The slurry of the invention can be applied separately orsimultaneously to the walls of the borehole to fill or plug theborehole, to the inside or outside surfaces of wellbore casing, or tolayers of sealant that have already set.

[0073] When the slurry is placed using canisters, the filled canistersare lowered into the borehole to the selected depth on a wireline(electric logging cable) or coiled tubing. The canisters can be jointsof HDPE on PVC pipe or other plastic or metal pipe adapted to containthe slurry, or any other suitably sized containers that can be fittedwith burst diaphragms or other openings through which the slurry can beextruded and that can be either retrieved or drilled from the borehole.Presently preferred are plastic or resin canisters because the inventionslurries do not bond to plastics or resins and can easily be extrudedfrom plastic canisters. Plastic canisters are more easily drillable andsometimes preferred so that the drill bit can be guided as it drillsthrough a canister left downhole. Canisters of HDPE are more flexiblethan PVC or metal and thus particularly suited for use in lateralwellbores. A canister sufficiently large to hold the total amount ofslurry to be applied is generally preferred, unless sequentialapplications of the slurry are being applied or additional slurry is tobe pumped from the surface down connecting coiled tubing.

[0074] Electric wire line equipment is often already at the drillingsite or readily available. Therefore, it is generally preferred to usethat manner of lowering a canister filled with invention slurry down thehole, or drill pipe if hole integrity is in question. The canister canbe any suitable container with any suitable way of extruding the slurryfrom the canister. Generally a submersible pump and piston is needed toextrude the slurry and a burst diaphragm or other equivalent exit forthe slurry is needed at the bottom of the canister.

[0075] In one example of a presently preferred embodiment of theinvention, a submersible electric pump is attached to an electric wireline with the pump fitted to the upper end of the slurry-carryingcanister thats lowered down a borehole. FIG. 1 shows a schematic of acanister 10 in a borehole 12 on a wire line 14. The attachment of thewire line 14 to the pump 16 is by means of a wire line cable head 18 orother suitable attachment mechanism affixed to the leading end of thewire line 14. The attachment of the pump 16 to the cannister 10 can beany suitable release mechanism if it is desired that the wire line 14and attached pump 16 be pulled from the borehole 12 without the canister10 after the canister 10 is emptied. Presently preferred is use of anelectromechanical release mechanism 20 that holds the pump 16 securelyinside the top end of the canister 10 but that is readily released whenit is desired to withdraw the wire line 14 and pump 16 from the borehole12 after the slurry has been extruded into the open hole, leaving onlythe drillable canister 10 behind in the borehole 12.

[0076] In this embodiment of the invention, the pump 16 is preferablyplaced in the top end of the canister 10 above a wiper plug 22, pistonor plate separating the slurry from water or drilling fluid above thewiper plug 22, piston or plate. The wiper plug 22, piston or plate willgenerally have seals 24 around its circumference as needed. The pump 16draws drilling fluid or water from the borehole 12 above the canister 10through an inlet port 26 to pump down against the top of the wiper plug22, piston or plate on top of the slurry in the canister 10 therebyextruding the slurry from the canister 10. A gap or space 28 between thepump 16 and the top of the wiper plug 22, piston or plate permits inflowof pressurized drilling fluid, mud, or water from the pump 16.

[0077] A relatively small pump can be used since the pressure is neededonly to push the slurry from the canister through the burst diaphragm orother exits onto the surfaces to be sealed or stabilized or into thehole to be plugged. It is important, however, that a pump capable ofpumping fluids with particulate matter be used since it is desired to beable to pump either drilling fluid that may have cuttings or to pumpwater that may have particulate additives. Depending upon the volume andconsistency of the slurry and the hydrostatic pressure of the formationor drilling fluid where the seal or plug is to be, applied, a pumpcapable of pumping from about 50 to about 200 psi is generally useful.

[0078] As shown in FIG. 1, canister 10 has burst diaphragm 30 attachedto or built into the end cap 32 as shown in FIG. 1. Alternatively,valves or other suitable slurry exits as a way of allowing the sealantto be released or extruded from the canister can be used. If desired,these may be positioned on all sides near the bottom of the canister todisperse the slurry more evenly about the borehole walls. When burstdiaphragm 30 is used, fluid pressure can be used to open the burstdiaphragm 30 and extrude the sealant from canister 10.

[0079] Generally, burst diaphram 30 is in an end cap 32 (that containsthe slurry in the canister) or other stop mechanism attached to thebottom of the canister 10. The end cap 32 prevents the wiper plug 22,piston or plate from overdisplacing the slurry by stopping the wiperplug 22, piston or plate at the bottom end of the canister 10 to preventthe pump 16 from pumping drilling fluid or water through the canister 10and into the borehole 12.

[0080] A low-pressure inflatable packer 34 installed around the outercircumference of the canister may be employed to centralize the canister10 in borehole 12 and to prevent slurry being extruded from the lowerportion or bottom of canister 10 from backing up around canister 10 andupward in borehole 12. Inflatable packer 34 can be inflated aftercanister 10 is positioned downhole by the same pump pressure being usedto extrude the slurry, and deflated after the slurry is placed by usingthe depressurization of the slurry or drilling fluid or by any othersuitable means.

[0081] After the slurry has been extruded from the canister, thecanister can be withdrawn from the borehole and, if needed, refilledwith more slurry and run into the borehole again to augment the slurrypreviously placed.

[0082] However, if the canister is sealed in the borehole or for someother reason it is desired to leave the canister down hole, this can bedone. This is generally practical because when the slurry sets up in thehole where it was extruded, it generally seals canister 10 in place,with canister 10 centralized in the borehole if inflatable packer 34 isused at the lower end of canister 10. After pump 16 is detached, it iswithdrawn from the hole along with the wire line 14 by use ofelectromechanical release mechanism 30, or other detachable or releasemechanism. The top of the canister generally can be fitted with conicaldrill bit re-entry guide 36 that also serves to centralize the top ofcanister 10 in borehole 12. A guided bore centralized drilling assembly,fitted on bottom with a small-diameter “stinger” designed to fit insidethe top of the plastic canister, is run into the hole. Conical re-entryguide 34 fitted to the upper end of the canister serves as a guide for adrill bit, or, more particularly, a drill bit fitted with a stinger, todrill down through the canister rather than being deflected into adeviated drilling path by a canister and set-up slurry that can beharder than the surrounding formation. The sealant-stabilized troublezone is then drilled out.

[0083] In another presently preferred embodiment of the invention, aslurry-carrying canister, with a submersible electric pump affixed tothe upper end, is lowered inside the drill pipe to the bottom of thedrill string on an electric wire line. This application of the inventioncan be used when it is preferable to leave the drill pipe in an unstablehole, such as when drilling through rapidly caving or sloughingformations, or where severe lost circulation is encountered with zonesof squeezing or swelling clays or other plastically deforming formationsoccurring above a loss zone.

[0084] An example of this embodiment of the invention is shownschematically in FIG. 2. Slurry-containing canister 10 is lowered downthe inside of drill pipe 38 on electric wire line 14 to a position justabove drill bit 40. The attachment of the bottom of electric wire line14 to the top of ump assembly 16 is by cable head 18, which containselectric pass-throughs.

[0085] The attachment of the pump assembly 16 to the canister 10 can beby any suitable attachment mechanism 20. The pump 16 draws drillingfluid or water from inside the drill pipe through the inlet port 26 andapplies pressure to the wiper plug 22, piston or plate, displacing thewiper plug 22, piston or plate downward thereby pressurizing the slurryand bursting the burst diaphragm 30 or other suitable pressure-openingmechanism built into the end cap 32 of the canister 10.

[0086] The slurry is forced through the fluid jets of the drill bit 40and into the borehole 12, sealing or plugging the lost-circulation zoneor filling and stabilizing the caving and washed-out borehole interval.Displacement of the slurry up and around the canister 10, in the annularspace between the canister 10 and the inside of the drill pipe 38, canbe prevented by a circumferential pressure-actuated inflatable-packer 34attached to the outside of the canister 10 which seals this annulus.

[0087] The end cap 32 attached to the bottom of the canister 10 containsthe slurry in the canister and prevents the wiper plug 22, piston orplate from overdisplacing the slurry by stopping the wiper plug 22,piston or plate at the bottom end of the canister 10 to prevent the pump16 from pumping drilling fluid or water through the canister 10 anddrill bit 40, and into the borehole 12.

[0088] After the slurry has been extruded through the jets in the drillbit 40 and into the borehole 12 but before the slurry starts setting up,the drill pipe 38 is lifted up several tens of feet off the bottom ofthe hole, or above the depth of the trouble zone, and then the emptycanister 10 and attached pump assembly 16 are withdrawn from the drillpipe 38. If additional quantities of slurry are required (e.g., to filla large washed-out interval of the hole), the above operations can berepeated one or more times with a refilled canister, again run throughthe drill pipe on a wire line.

[0089] Coiled tubing is the basis of three other methods of applying theinvention sealants: (a) use of coiled tubing to lower a filled canister;(b) use of coiled tubing to lower a filled canister and provideadditional flow of invention slurry into the canister; and (c) use ofcoiled tubing without a canister to provide a flow of invention slurrydownhole.

[0090] “Coiled tubing” refers to a flexible steel tube, with a diameterfrom about ⅝″ to about 2″ and a length exceeding the depth to which thetube is to be inserted in the borehole or inside the drill pipe, whichis rolled up on a large diameter spool. In methods (a) and (b), acanister containing the slurry is attached to the leading end of thecoiled tubing.

[0091] The coiled tubing is unrolled from the spool as it is put downeither the wellbore or down through the string of drill pipe. If thereis risk of cave-in of the wellbore, then it may be desirable to leavethe string of drill pipe down the hole and put the coiled tubing with orwithout a canister down the drillstring and extrude the sealant outthrough the jets in the bit. In either case, with or without a canister,when operating inside drill pipe, there needs to be a provision, eithermechanical or hydraulic, to seal the annular gap between the canister orcoiled tubing and the inside diameter of the drill pipe so that thesealant does not flow upwards past the canister rather than downward andout through the jets in the drill bit.

[0092]FIG. 3 shows an example of the use of a canister on coiled tubingto apply the invention sealant to form a ceramic “casing” that adheresto, penetrates, and lines the inside diameter of the borehole. In thisexample, a zone of swelling or squeezing clays or plastically deformingserpentine formation is stabilized and repaired using the inventionapparatus and an invention method. First, the trouble zone 50 isunderreamed from the initial diameter of the drilled wellbore 52 usingany suitable drilling equipment known in the art to form an underreamedsection of wellbore, also 50. After removing the underreaming assemblyfrom the hole, an open-ended full-gauge blade reamer assembly 54 is runin the hole to the top of the trouble zone 50 to be stabilized.

[0093] Then a drillable canister 56, similar to that described above andshown in FIG. 2 is filled with slurry and lowered through the drill pipe58 and reamer assembly 54, which extends only to the top of theunderreamed section of wellbore 50. The top of the canister 56 isattached to a small-diameter coiled tubing 60 using a running andrelease mechanism 62 with one or more shear pins or any other suitablerelease mechanism.

[0094] The lower end of the canister 56 is fitted with an end cap 64having thereon a burst diaphragm 66. The slurry is extruded through theburst diaphragm up and around the canister 56 into the underreamedsection of wellbore 50. After the slurry is extruded from the canister56 and allowed to partially set up, the coiled tubing release mechanism62 is activated and the coiled tubing 60 is withdrawn from inside thedrill pipe. Then, the drill pipe 58 with the blade reamer assembly 54 isremoved from the borehole before the slurry sets up further and bindsthe blade reamer assembly 54 in the borehole. The canister 56 is leftdownhole.

[0095] The canister 56 is subsequently used as a guide for redrillingthe borehole as explained in the description of FIG. 1. After the slurryhas had time to set up, but is not yet completely cured into adifficult-to-cut ceramic, a guided-bore centralized drilling assembly,fitted on bottom with a small-diameter “stinger” designed to fit insidethe top of the canister, is run into the hole and the sealant-stabilizedtrouble zone is drilled out to the full borehole diameter. Afterwithdrawing the guided-bore drilling assembly from the borehole, thedrilling program can be resumed below the ceramic “cased” trouble zone.

[0096]FIG. 4 shows use of the invention apparatus and the methoddescribed with regard to FIG. 3 for stabilizing and repairing a zone ofunconsolidated, loose, or friable formation in which caverns or washoutshave occurred. In FIG. 4 there is shown a zone of caving 70 withwashouts that is partially bifurcated by a layer of harder rock 72 in aborehole. An open-ended full-gauge blade reamer assembly 74 or any othersuitable tool is used to centralize the drillstring just above thewashout zone.

[0097] A drillable canister 76 filled with invention slurry is thenlowered down the drillstring on a small-diameter coiled tubing 78 filledwith enough additional slurry (with a wiper plug on top) toapproximately fill the cavernous zone when extruded from the bottom ofthe canister by pressurizing the coiled tubing from the surface. Thecanister 76 is sized so that it passes through the open end of thedrilling assembly and is long enough to reach the bottom of the troublezone.

[0098] The canister 76 is rapidly lowered on the coiled tubing 78through the drill pipe 80 to the bottom of the caving zone 70. Thecoiled tubing 78 is pressured up enough to open a burst diaphragm 82 inan end cap 84 on the lower end of the canister 76, thereby extruding theslurry out the bottom of the canister and back up around the outside ofthe canister, filling the annular gap 86 between the canister and thecavernous borehole wall. The small inside diameter of the canister 76and the smaller inside diameter of the coiled tubing 78 affords a veryaccurate control of the volume of the slurry extruded so that thecavernous interval 70 can be completely filled, but not overfilled.

[0099] After allowing sufficient time for the slurry to set up, thecoiled tubing 78 is released from the canister 76 using any suitabletechnique, such as shear pins or a pressure-activated release mechanism,and removed from the borehole. The canister 76 is left downhole and thedrill pipe 80 and blade reamer assembly 74 are then removed from theborehole. Finally, a guided bore centralized drilling assembly, fittedon bottom with a small-diameter stinger designed to fit inside the topof the plastic canister, is run into the hole and the sealant-stabilizedtrouble zone is drilled out.

[0100] Alternatively, the coiled tubing without a canister is run to theselected depth through open-ended drill pipe and the invention slurriesare pumped down and out of the coiled tubing to seal or stabilize thewalls of the borehole or into the drilling fluid in the borehole to forma plug filling the borehole.

[0101] When the slurry is pumped from the surface through asmall-diameter coiled tubing that is fitted with a check valve orsimilar device on bottom, and extruded at the trouble zone, anothersignificant advantage of the invention accrues. Since the interiorvolume per unit length of small-diameter coiled tubing is very muchsmaller than the corresponding volumes of either the borehole or thedrill pipe, a very considerable control over the exact amount of slurryapplied to the trouble zone is gained.

[0102] In addition, when using coiled tubing, if the trouble zoneinvolves severe lost circulation, the slurry can be “pumped” down thecoiled tubing and then extruded from the bottom of the coiled tubingusing a combination of compressed air and water as the motive force, sothat the very significant overpressure due to the hydrostatic head of acorresponding column of pressurizing water inside the coiled tubing canbe avoided. This avoidance of overpressuring a zone of severe lostcirculation permits the slurry to stay in its intended location in theborehole as it sets up rather than being overdisplaced much farther outinto the formation or fracture zone, as commonly happens when cement ispumped down drill pipe from the surface.

[0103] A wiper plug can be inserted above the slurry to give a pressurepulse when the air- or fluid-driven plug hits bottom, thereby signalingthe driller that the slurry has all been extruded out the bottom of thecoiled tubing.

[0104] In another alternative embodiment of the invention, the drillpipe may be removed from the borehole and the naked coiled tubing putdown the borehole. An additional advantage accrues when running coiledtubing naked into a borehole. Because of the small diameter of thecoiled tubing, it can more easily be “washed” to bottom or to thelocation of the trouble zone by the pressurized jet of drilling fluidbeing pumped out the end of the coiled tubing.

[0105] Generally, except for very shallow boreholes, it is much moreeffective and safer, and also less costly, to place the slurry at thetrouble zone through coiled tubing or by extruding the slurry from acanister run on coiled tubing or on an electric wire line. This isbecause of the increased accuracy and ease of placement using thesemethods as compared to direct openhole or drill pipe placement of theslurry by pumping from the surface.

[0106] However, in some exceptional circumstances such as when it isnecessary to quickly stabilize a hole that is caving in order to savethe hole, or when there is a dramatic loss of circulation and there isno coiled tubing equipment or wire line with a sealant canister at therig site, the invention slurry can be pumped directly down the boreholeor, more preferably, down the drill pipe. If the sealant is to beapplied by pumping slurry directly down the drill pipe, it is generallypreferable to pump in the selected amount of slurry (for example, about200 gallons), then put in a wiper plug after the slurry. Drilling fluidor a mixture of drilling fluid and water is then pumped in above thewiper plug to push the slurry down the drill pipe and through the jetsin the drill bit if the drill bit has not been removed from the drillstring. To maintain the subhydrostatic pressure that is needed toprevent overdisplacement when dealing with a severe lost-circulationproblem, compressed air can be applied on top of the drilling mud andwater above the slurry, to reduce the hydrostatic head of the fluid inthe drill pipe.

[0107] After the placed slurry has had time to set up, it may bepossible to dissolve the sealant out of the drill bit jets with acid ifthe bit was on the drill string when the slurry was put down the hole.More likely, the drill bit may have to be sacrificed. If there was nodrill bit on the drill string or if the slurry was pumped directly downthe hole without the drill string, then the hole is redrilled as itwould be if it had been plugged with cement.

[0108] Whatever placement method is used, after application to thelocation where the seal, wellbore stabilization, or plug is desired, theslurry sets up or cures in place. The invention slurries can set up orharden even in an aqueous environment, such as in a wellbore filled witha water-based drilling fluid. Setting of the invention slurries appearsnot to be sensitive to hydrocarbons or saline environments that occur insome drilling operations.

[0109] The slurry sets up to form the sealant in the open borehole, orbetween a steel pipe or casing set in the borehole and the surroundingformation, or between two separate concentric steel pipes installed inthe borehole and the surrounding formation, or between itself andpreviously set-up stages of slurry in the borehole, depending upon thepurpose for using the sealant and where it is extruded. The slurryexpands slightly and tightly adheres to and adsorbs into and seals anyopen fractures within the surrounding formation that intersect the wallof the borehole or any open porosity in the surrounding formation,thusly forming a tight seal in the pores or fractures in the formation,between the formation and casing, or between casings, or tightly adheresto previously set sealant. It also bonds to the steel pipe or casing,forming an impervious and structurally sound seal with mechanicalsupport characteristics superior to those of portland cement.

[0110] Curing times can range from as little as a matter of minutes to anumber of hours. For most invention slurries at ambient temperature andpressure, and depending upon whether curing retardants are used and theamounts of retardants used, the curing time generally ranges from about20 minutes to about four hours.

[0111]FIG. 5 is a graph of the increase in compressive strength of theinvention sealant as a function of time. It can be seen that there is adramatic increase in the compressive strength during the first five daysafter the sealant has begun to solidify.

[0112] As the sealant continues to cure, the increase in compressivestrength is more gradual, although continuing improvements have beenobserved for times up to 45 days or longer.

[0113] The invention sealants have compressive strengths between about3500 psi and 12,000 psi, depending upon whether a second phase materialis added and, if so, depending upon how much and which material is used.The compressive strengths of the invention sealants compare favorablywith that of conventional cement that has a compressive strength ofabout 4000 psi.

[0114] The chemically bonded ceramic sealants of this invention havecovalent and ionic bonding, and hence are very hard ceramic materials.They are insoluble dense solids when set up and are durable in hightemperature and corrosive environments.

[0115] The invention sealants have porosities in the range fromvirtually 0 to about 5 percent, depending upon particle sizes of thepowders used and, if used, the kinds and particle sizes of fillers. Thisporosity is much lower than the typical porosity of portland cement,which generally has a porosity in the range from about 10 to about 20percent. The set material has a generally nonporous finish and isimpermable to liquids including aqueous-based and hydrocarbon liquidsand gases.

[0116] The invention sealants are environmentally safe because allcomponents used in the slurries that set up to form the sealants areinorganic and nonhazardous oxides or hydroxides. They are eitherconventional powders or phosphates typically used in fertilizers anddetergents. There are no clean-up problems associated with the inventionsealants because the invention sealants are readily soluble in eitherphosphoric acid or commercially available acids such as hydrochloric orsulfuric acid solutions with low pH. Sealants that are drilled arrive atthe surface as small particles or chips along with any cuttings in thedrilling mud recirculated to the surface.

[0117] This invention provides methods and sealant materials toeffectively accomplish the cementing of casing, fluid diversion,borehole wall sealing, borehole wall stabilization, and boreholeplugging in vertical, deviated or horizontal wells on and offshore. Thedownhole sealants of this invention can be used to solve wellboreproblems during the drilling and completion of oil, gas, geothermal,water and other types of wells.

[0118] Borehole walls can be unstable due to either continual caving orsloughing of the poorly consolidated or loose and friable sediments orvolcanics (e.g., soft pumice deposits) being drilled, or formationsbeing comprised of swelling or squeezing clays or plastically deformingserpentines. Swelling or squeezing clays or plastically deformingserpentines can severely reduce the borehole diameter or completelyclose off the borehole in less than a day of time, making repair andstabilization of the borehole mandatory before drilling can continue.Often, when these difficult drilling situations are encountered, theonly currently satisfactory remedial operation is to run and cement astring of casing through the trouble zone as quickly as possible.However, in deep offshore drilling situations in particular, the runningof an additional string of casing can add millions of dollars to thecost of a single production well. Embodiments of the invention such asthat shown in FIG. 3 can be used to place a ceramic casing through thetrouble zone, thereby solving these types of problems.

[0119] In another problem solved by use of the invention, the walls of aborehole that is being drilled through an unconsolidated, loose, orfriable formation, have caved in to form caverns or wash-outs. Thewashed-out borehole needs to be stabilized and then filled with sealantbefore drilling can proceed. An example of this situation is shown inFIG. 4 described above.

[0120] Another important application for the invention slurries andsealants is stopping loss of circulation and sealing lost-circulationzones, particularly if the pore pressure of the loss zone issignificantly subhydrostatic (underpressured). If the formation issignificantly underpressured and contains major fractures or caverns, oris extremely porous, drilling fluids can be rapidly lost out into theformation. With loss of circulation and hydrostatic borehole pressure,there is much less drilling fluid pressure to stabilize the boreholewall and no cuttings will be recirculated to the surface. With nocirculation of cuttings, the chances of getting the drilling assemblystuck in the hole are greatly increased.

[0121] Rather than sometimes futile attempts to stop severe loss ofcirculation by putting lost-circulation materials into the drillingfluid or by attempting to cement the loss zone from the surface, acanister of invention slurry can be run down the borehole or the drillpipe on a wire line or on coiled tubing and extruded to seal upfractures, large pores or small caverns in the formation. If there arecaving or swelling formations above the lost-circulation zone, thepreferred sealing method (if the drillstring has been removed from thehole) is to run coiled tubing fitted with a nozzle on the downhole end.The small diameter coiled tubing can be used to wash its way down theborehole through the upper caving or swelling formations to the losszone by using a jet of drilling fluid. Once the coiled tubing is at theloss zone, invention slurry mixed at the rig site to the selectedviscosity can be pumped down the coiled tubing in whatever amounts andpressures are needed to seal or plug the lost circulation zone. Sincethe level of the drilling fluid in the borehole will typically besignificantly below ground level but above the loss zone, thehydrostatic pressure of the slurry needs to be balanced with thehydrostatic head of the water and/or drilling fluid above the loss zoneso as to not overdisplace the slurry. This can be accomplished byadjusting the amounts and pressures of the slurry being pumped down thecoiled tubing. One way of controlling slurry extrusion pressure moreexactly is to slowly pump air into the coiled tubing behind the slurryso as to slowly extrude the slurry without increasing the hydrostatichead of the slurry.

[0122] After the appropriate amount of slurry has been introduced intothe lost circulation zone, the coiled tubing is pulled from the boreholebefore the slurry sets and binds the coiled tubing. If drilling isresumed before the sealant completely cures and is still softer than thesurrounding formation, drilling usually can be resumed without use ofadditional equipment to centralize the drill bit.

[0123] If zones of water inflow are sequentially sealed in accordancewith this invention during drilling, the borehole can be maintained at asignificantly subhydrostatic pressure condition by using air, foam, oraerated mud as the drilling and circulating fluid, without the inflow ofsignificant amounts of water. Then, underbalanced drilling methods usingpercussive drilling assemblies and downhole motors, deployed on eitherdrill pipe or coiled tubing, can be employed to greatly increase ratesof penetration and thereby reduce the overall costs of drillingprograms.

[0124] The invention sealants are ideal for plugging holes for fluiddiversion. Fluid diversion is a procedure or operation to promoteuniform treatment of a long heterogeneous interval with two differenttreating fluids, each of which is directed sequentially to a differentarea in a well. Effective diversion is more difficult for a highlydeviated or horizontal well than for a conventional vertical well. Thecombination of wellbore angle, formation type, interval length, and theexistence of natural fractures complicates efforts to divert treatmentfluids.

[0125] Fluid diversion is critical to the success of well treatmentssuch as matrix acid treatments, matrix solvent treatments and water/gasshut-off treatments. An effective diversion technique is accomplished byplugging a zone temporarily, forcing the treatment fluids into otherregions, and then removing the plug after the treatment. Plugs ofsealants of the present invention can easily be removed by redrillingthrough the cured or partially cured sealant.

[0126]FIGS. 6a and 6 b show a schematic of a diversion process in acased and perforated vertical well. In FIG. 6a the major portion of theflow of treatment fluid is going past a first sand zone that is damaged,past a shale zone and going out into a second sand zone. In FIG. 6b,after the second sand zone has been plugged or sealed with inventionsealant, the major portion of the flow of treatment fluid is divertedinto the first sand zone.

[0127] When invention sealants are used to both seal and support thejunction of a lateral (deviated) wellbore with the primary wellbore in apetroleum or geothermal application, the slurry is extruded from adrillable canister that can be run on either a wire line or coiledtubing as shown in FIG. 7.

[0128]FIG. 7 is a schematic of a lateral wellbore 100 drilled from thecased main wellbore 110 within an interval 112. The junction of thelateral wellbore 100 with the main wellbore 110 can be constructed inthe following manner. A retrievable whipstock 114, coated with non-stickplastic on its sides so that the invention slurry will not adhere to thewhipstock 114 and bond it to the steel casing 116, is oriented andlocked into the casing 116 with a suitable casing locking device 118(e.g., an anchor) built into the lower part of the whipstock 114. Amill, run on drill pipe, is then run into the hole and using thewhipstock 114 as a guide, a window 120 is cut in the steel casing 116permitting the drilling of a lateral wellbore 100 only slightly smallerthan the inside diameter of the cased main wellbore 110. Then, afterremoving the mill assembly used to cut the window 120, a stub of thelateral wellbore 100 is drilled some 30 to 60 feet out into thesurrounding rock, again using the whipstock 114 as a guide to bothdeflect and control the direction of the drill bit. The drillingassembly is then removed from the wellbore and an underreaming drillingassembly is used to enlarge the diameter of the stub lateral 100 toabout 6 inches greater than the original drilled diameter of the stublateral 100. Then, the underreaming assembly is removed from thewellbore.

[0129] A drillable canister 122 filled with invention slurry is loweredinto the drilled stub of the lateral wellbore 100 on a coiled tubing 124that is attached to the canister 122 with a shear pin fixture or anysuitable pressure release mechanism. The top of the canister 122 isconfigured as an entry guide or has attached thereto an entry guide 126to accept a stinger on the bottom of a drilling assembly while thebottom of the canister 122 is centralized by the short length ofstandard diameter lateral stub remaining below the underreamed section.The lower end of the canister 122 is fitted with an end cap 128 having aburst diaphragm 130 in the bottom of the end cap 130. Aluminumbow-centralizer springs 132 or any other suitable means can be used toposition and centralize the canister 122 within the drilled andunderreamed stub of lateral wellbore 100.

[0130] After the canister 122 is lowered into the drilled stub of thelateral wellbore 100, the slurry is extruded into the underreamedportion of the lateral wellbore 100 and up into the adjacent portion ofthe main wellbore 110, and then the coiled tubing 124 released from thecanister 122 and pulled from the wellbore. Then equipment such as adrill bit with a stinger assembly is used to drill through thecentralized canister 122.

[0131] In an improvement over use of portland cement for sealing andsupporting a lateral junction, the sealant forms a section of ceramic“casing” that: (a) provides an impermeable, pressure-tight seal at thelateral junction with the casing in the primary wellbore; (b) tightlyadheres to and seals the surrounding formation, thereby providing amechanical support with high compressive and shear strength forsubsequent drilling operations; and (c) allows the lateral to be drilledat full diameter without the need for inserting casing in the lateralborehole until the borehole is ready for completion with a string ofproduction tubing. In addition, after being emptied, the centralizedplastic canister that contained the slurry forms an excellent drillingguide to allow the “gun-barrel” drilling out of the sealant from thestub of the lateral junction leaving an approximately uniform ceramic“casing” wall thickness.

[0132] One particularly important application for the invention sealantand method is use as a means of fluid diversion in wells where directaccess to the formation is blocked by a sand control device.

[0133] Highly deviated or horizontal wells are sometimes completed usinga slotted liner gravel pack, or sand screen, to stabilize the wellborewalls and to limit flow of unconsolidated, loose or friable sand fromthe producing formation into the wellbore while at the same timeallowing the flow of gas or liquids from the producing formation intothe wellbore during production of the well. These wellbore completionsare referred to as sand-control completions.

[0134] Such sand-control methods complicate fluid diversion efforts byallowing fluids to flow outside the lined wellbore proper. Thesealternate flow paths for fluid occur between the formation and theslotted liner or sand screen, or within the gravel pack itself.

[0135]FIG. 8 shows a schematic of damaged, non-productive and undamagedintervals in a slotted-liner horizontal completion before use of aninvention sealant and method. The heavy arrow at the left of the drawingindicates direction of flow of treatment fluid or slurry during asealing or plugging operation. The small vertical arrows along the linerand the two long essentially horizontal arrows in the annulus betweenthe liner and the formation indicate flow of treatment fluid withoutdiversion.

[0136] For the specific slotted-liner horizontal completion situationshown in FIG. 8, the sealant is extruded in place to provide aneffective fluid diversion technique. The invention slurry can beextruded from a coiled-tubing-deployed canister made of a material(e.g., HDPE or PVC) that can easily be drilled out. The canister ispositioned in a non-productive interval between the damaged andundamaged zones of the wellbore and adjacent to a slotted section of theliner. A canister that is sealed at the bottom and fitted with an arrayof low-pressure burst diaphragms along its length of approximately 30feet is generally useful. Slurry with the consistency of thin caulkingcompound is pressure extruded to fill both that portion of the slottedliner around the canister and to also flow through the slots and fillthe annulus between the slotted liner and the formation.

[0137] When set, the sealant tightly adheres to both the formation andthe steel liner, sealing both the bore of the liner and the annulusbetween the liner and the formation. In the specific example of theinvention shown in FIG. 8, after treatment to remediate the damaged zoneupstream of the sealed borehole, the only operation needed would be todrill out the bore of the slotted liner to regain access to bothintervals of the wellbore since the sealant in the annulus outside theslotted liner (across the intervening nonproductive interval) does nothave to be removed.

[0138] However, if there is a very limited wellbore distance between thedamaged and undamaged productive intervals as shown schematically inFIG. 8, it may be necessary to actually plug off the upper portion ofthe undamaged production interval with extruded sealant to produce aneffective diversion of the treatment fluid to the damaged productioninterval. Then it is subsequently necessary to remove the sealant fromthe liner bore by drilling and to then also remove the sealant from theslots in the liner, the annulus between the liner and the productiveformation, and a shallow distance into the part of the productionformation forming the borehole. This is done by dissolution of thesealant using an extruded dose of a concentrated acid, such asphosphoric acid. The acid is extruded from a coiled-tubing-deployedcontainer fitted with burst diaphragms to accurately place the acid overthe sealed interval of slotted liner, to regain access to all of the“lower” productive interval.

[0139] For a situation involving a gravel pack or sand screen, thediversion job becomes more difficult, but is still doable using acoiled-tubing-deployed canister. For these situations, the drillablecanister is centralized within the screen section so that after sealingoff the interval, the empty canister is used as a guide for drilling outthe inside of the gravel pack or screen.

[0140] The invention compositions and methods can be very important inoffshore drilling operations, particularly in deep or rough seas.Typically during the initiation of almost all deep ocean drillingoperations, a string of “conductor” pipe is cemented through the verysoft and friable muds, silts and sands typically occurring on the oceanfloor. The bottom of the string of conductor pipe can advantageously becemented in place and stabilized using invention compositions andmethods. An invention slurry is extruded from a canister run on coiledtubing after the string of conductor pipe has been set in position. Thebottom of the string of conductor pipe is fitted with a speciallydesigned “cementing shoe” that has a lock-in device on the inside toaccept a mating mandrel assembly on the bottom of the canister ofinvention slurry.

[0141] After the selected amount of slurry has been extruded out thebottom of the canister and up and around the lower portion of theconductor pipe as well as out into the pores of the surrounding looseand friable sediments and allowed to set up, the surrounding softsediments are stabilized and the sealant tightly adheres to the outsideof the conductor pipe, forming a mechanically supported and sealed“anchor” for the conductor pipe to the surrounding sediments.

[0142] This cementing operation could also be accomplished using drillpipe, but the use of a canister run on coiled tubing offers both a muchgreater degree of control and a faster overall cementing operation.

[0143] The following examples will demonstrate the operability of theinvention.

EXAMPLE I

[0144] In a bench top demonstration of an invention slurry and sealant,a slurry was mixed and allowed to set up in a beaker filled with water.

[0145] An invention slurry was prepared by combining a total of 200 g ofclass-F fly ash, calcined magnesium oxide and monopotassium phosphate ina 60:9:31 ratio. The 200 g mixture was stirred in 20 g of water forabout 20 minutes. The slurry had started reacting and had formed a thickpaste. The thickened slurry was then poured into a beaker and allowed toset for about 60 minutes.

[0146] After the slurry had solidified, hot water at a temperature of90° C. was poured onto the set slurry. The beaker was maintained at 90°C. on a hot plate for about 30 minutes. The slurry did not dissolve orreact in the water.

[0147] Then 220 g of a second slurry was prepared in the same manner asthe first slurry with the same ratio of components.

[0148] After about 30 minutes the second slurry had started to react andthicken. The second slurry was poured into the hot water in the beakerand was observed to be immiscible with the water. The second slurrydisplaced water and sank to the top of the hardened first slurry. Thesecond slurry was allowed to cool for two hours. After two hours thewater was decanted out of the beaker.

[0149] The second slurry had bonded intimately with the first slurry,forming a monolith. The monolith adhered to the glass beaker due toslight expansion that occurred during setting of the slurries.

EXAMPLE II

[0150] In another bench top demonstration of the invention, setting timeas a function of temperature was measured.

[0151] A 220 g portion of slurry was prepared in the same manner as theslurries in Example I and in the same proportions of components. Thebeaker in which the slurry was prepared was then lowered into a waterbath maintained at a temperature of 60° C. and the time of setting wasmeasured by determining the time that the slurry took to form a hardenedmonolith.

[0152] The procedure was repeated at temperatures of 70° C., 80° C., and90° C. Each time the setting time was measured. Setting times decreasedas temperatures increased, ranging from a setting time of about 70minutes at 60° C. to a setting time of about 35 minutes at 90° C. Theresults of this test of an invention slurry are shown in the graph ofFIG. 9.

EXAMPLE III

[0153] An invention slurry prepared in the same manner as that preparedin Example I and having the same ratio of components was poured intopolyethelene beakers containing sandstone, limestone and granite rocks.The rocks were several inches in size and of the sort typically found inoilfield drilling environments.

[0154] The slurry in each of the beakers was allowed to set for a day,during which time it formed into monoliths with the rocks as inclusions.The monoliths were removed from the beakers.

[0155] A diamond tipped saw was used to cut the monoliths into crosssections. In each case the slurry had formed into a sealant thatencapsulated the rocks with no gaps at the interface between the rocksurfaces and the slurry. In fact, the slurry had penetrated into thepores in the surfaces of the rocks forming a tight bond and excellentseal with the rocks. A cross section of this is shown in the photographof FIG. 10.

[0156] While the methods and compositions of this invention have beendescribed in detail for the purpose of illustration, the inventivemethods and compositions are not to be construed as limited thereby.This patent is intended to cover all changes and modifications withinthe spirit and scope thereof.

Industrial Applicability

[0157] The slurries, sealants and methods of this invention can be usedfor treating or repairing boreholes at specific depths; sealing zones ofinflow from formations or outflow of drilling fluids; diversion offluids for treatment of oil, gas, geothermal and water wells; andtemporarily or permanently plugging wellbores at specific depths.

[0158] The above examples of the present invention have been presentedfor purposes of illustration and description and are not intended to beexhaustive or to limit the invention to the precise form disclosed, andobviously many modifications and variations are possible in light of theabove teaching. The embodiments were chosen and described in order tobest explain the principles of the invention and its practicalapplication to thereby enable others skilled in the art to best utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the claims appended hereto.

What is claimed is:
 1. A method of treating a borehole, comprising thesteps of: (a) preparing slurry comprising oxide or hydroxide, phosphate,and water; (b) applying the slurry at a selected depth in a borehole;and (c) allowing the slurry to set up to form a sealant.
 2. The methodof claim 1, wherein the oxide or hydroxide is selected from the groupconsisting of MgO, MnO, Al(OH)₃, Al₂O₃, FeO, Fe₂O₃, Fe₃O₄, ZnO, Zr(OH)₄,ZrO₂, Y₂O₃, La₂O₃, VO₃, CrO, CoO, PbO, Nd₂O₃, TiO₂, CaSiO₃, and mixturesthereof.
 3. The method of claim 1, wherein the oxide comprises magnesiumoxide.
 4. The method of claim 1, wherein the oxide comprises zinc oxide.5. The method of claim 5, wherein the phosphate comprises the formulaA(H₂PO₄)_(n) wherein A=hydrogen, alkali metal, calcium, aluminum orammonium; wherein n is a number from 1 to
 3. 6. The method of claim 1,wherein the phosphate is selected from the group consisting ofphosphoric acid, NaH₂PO₄, KH₂PO₄, (NH₄)H₂PO₄, AlH₃(PO₄)₂, and mixturesthereof.
 7. The method of claim 1, wherein the phosphate comprisesKH₂PO₄,
 8. The method of claim 1, wherein the phosphate comprisesNaH₂PO₄.
 9. The method of claim 1, wherein the oxide comprises calciumoxide and the phosphate comprises Ca(H₂PO₄)₂.
 10. The method of claim 1,wherein the oxide or hydroxide is present in a stoichiometric amountrelative to the phosphate.
 11. The method of claim 1, wherein the oxideor hydroxide is present in an amount in the range from about 18 to about60 weight percent and the phosphate is present in an amount in the rangefrom about 40 to about 82 weight percent based upon total weight of theoxide or hydroxide and the phosphate.
 12. The method of claim 1, whereinthe oxide or hydroxide is present in an amount in the range from about20 to about 50 weight percent and the phosphate is present in an amountin the range from about 50 to about 80 weight percent based upon totalweight of the oxide or hydroxide and the phosphate.
 13. The method ofclaim 1, wherein the oxide or hydroxide is present in an amount in therange from about 22 to about 34 weight percent and the phosphate ispresent in an amount in the range from about 66 to about 78 weightpercent based upon total weight of the oxide or hydroxide and thephosphate.
 14. The method of claim 1, wherein the water is present in anamount in the range from about 25 to about 60 weight percent based upontotal weight of the slurry.
 15. The method of claim 1, wherein the wateris present in an amount in the range from about 30 to about 50 weightpercent based upon total weight of the slurry.
 16. The method of claim1, wherein the water is present in an amount in the range from about 30to about 35 weight percent based upon total weight of the slurry. 17.The method of claim 1, wherein the slurry further comprises a retardantthat retards the set up of the slurry.
 18. The method of claim 17,wherein the retardant is selected from the group consisting of boricacid, citric acid, oleic acid, and organic retardants containing atleast one inorganic component.
 19. The method of claim 1, wherein theslurry further comprises reinforcing material.
 20. The method of claim19, wherein the reinforcing material is selected from the groupconsisting of glass fibers, chopped glass strands, mica, silica,aramids, carbon fibers, alumina, hollow glass spheres, hollow silicaspheres, perlite, vermiculite, metal fibers, polymer fibers, copolymerfibers, silicate containing materials, and mixtures thereof.
 21. Themethod of claim 20, wherein the reinforcing material is present in anamount in the range from about greater than 0 to about 15 weightpercent, based upon total weight of the slurry.
 22. The method of claim1, wherein the slurry further comprises an additive that decreases theporosity of the sealant.
 23. The method of claim 22, wherein theadditive is selected from the group consisting of glass-formingsilicates, sodium compounds, fly ash, polymers and mixtures thereof. 24.The method of claim 23, wherein the additive comprises calcium silicate.25. The method of claim 23, wherein the additive comprises fly ash. 26.The method of claim 22, wherein the additive to decrease porosity ispresent in an amount in the range from greater than 0 to about 80 weightpercent based upon total weight of the non-aqueous slurry components.27. The method of claim 22, wherein the additive to decrease porosity ispresent in an amount in the range from about 10 to about 70 weightpercent based upon total weight of the non-aqueous slurry components.28. The method of claim 22, wherein the additive to decrease porosity ispresent in an amount in the range from about 2 to about 20 weightpercent based upon total weight of the non-aqueous slurry components.29. The method of claim 1, wherein the slurry further comprises asurfactant.
 30. The method of claim 29, wherein the surfactant isselected from the group consisting of gas generating agents, metal oxideexpanding agents, calcium sulfate hemihydrates and mixtures thereof. 31.The method of claim 30, wherein said surfactant is present in an amountin the range from greater than 0 to about 10 weight percent based upontotal weight of said slurry.
 32. The method of claim 1, wherein thewater comprises salt water.
 33. The method of claim 1, wherein the watercomprises seawater.
 34. The method of claim 1, wherein the watercomprises brine.
 35. The method of claim 1, further comprising the stepof: (d) drilling through the sealant.
 36. The method of claim 1, whereinthe slurry is applied by lowering a canister containing the slurry downthe borehole and then extruding the slurry from the canister into theborehole.
 37. The method of claim 36, wherein the canister is loweredinto the borehole on an electric wire line.
 38. The method of claim 36,wherein the canister is lowered into the borehole on coiled tubing. 39.The method of claim 38, wherein the coiled tubing is in fluidcommunication with the canister.
 40. The method of claim 36, wherein thecanister is lowered into the borehole through drill pipe.
 41. The methodof claim 1, wherein the slurry is applied by pumping it down theborehole through coiled tubing.
 42. The method of claim 1, wherein theslurry is pumped down the borehole through drill pipe.
 43. The method ofclaim 1, wherein the slurry is pumped directly down the borehole. 44.The method of claim 1, further comprising repeating steps (a) and (b).45. The method of claim 36, further comprising withdrawing the canisterfrom the borehole.
 46. The method of claim 36, further comprisingdrilling through the canister after forming the sealant.